【LeetCode & 剑指offer 刷题笔记】目录（持续更新中...）
3. Longest Substrleftng Without Repeating Characters
Given a string, find the length of the
longest substring
without repeating characters.
Examples:
Given
"abcabcbb"
, the answer is
"abc"
, which the length is 3.
Given
"bbbbb"
, the answer is
"b"
, with the length of 1.
Given
"pwwkew"
, the answer is
"wke"
, with the length of 3. Note that the answer must be a
substring
,
"pwke"
is a
subsequence
and not a substring.
//找字符串中的最长无重复字符的子串
/*
方法：Sliding Window
本质是枚举法
O(n)
*/
#include <unordered_set>
#include <algorithm>
class
Solution
{
public
:
int
lengthOfLongestSubstring
(
string s
)
{
unordered_set
<char> set; //用hash表存滑动窗中的数，方便查找是否有重复的数（用vector应该也可以，只不过hash表如果查找得到元素时效率高一点）
int
left
=
0
,
right
=
0
;
//双指针，指向子串区间的左右两端点
int
max_length
=
0
;
while
(
right
<
s
.
size
())
{
if
(
set
.
find
(
s
[
right
])
==
set
.
end
())
//如果不是重复字符，插入字符，更新最大长度
{
set
.
insert
(
s
[
right
++]);
//插入右边元素，右指针加一
max_length
=
max
(
max_length
,
int
(
set
.
size
())); //由于max函数只能对同类型的进行比较，这里强制转换
}
else
//如果为重复字符，则移除区间首字符，直到set中不再含此字符为止（会多次判断，多次执行移除操作）
{
set
.
erase
(
s
[
left
++]); //移除左边元素，左指针加一
}
}
return
max_length
;
}
};